1. Field of the Invention
This invention relates generally to the field of seismic prospecting and more particularly to transportable apparatus for injecting an acoustic pulse into the earth.
2. Description of the Prior Art
The invention to be described constitutes an improvement in transportable acoustic pulse generators of the type generally disclosed and illustrated in commonly-assigned, U.S. Pat. No. 4,284,165 entitled Acoustic Pulse Generator and filed Dec. 28, 1979. The generator described therein includes an upstanding cylindrical housing within which an impact mass is slidably supported in an upper firing position by an electrically controlled latch. A target plate is positioned on the ground beneath and spaced from the impact mass. Compressed gas is provided from high volume accumulators interconnected with large area ports penetrating the side wall of the housing near its top, the ports being normally blocked by the piston. Quick release of the latch admits gas within the housing through the ports, triggering the downward thrust of the impact mass to strike the target plate and to thereby generate an acoustic pulse.
In this prior art device the housing is adapted to be mounted in fixed relation to the framework of a transporting vehicle such as a truck. Experience has shown that the upward recoil force exerted against the housing as a result of the operation of the generator may cause the transporting truck to bounce on its spring suspension, with consequent danger of upset or damage to both truck and generator. This is of particular concern with impacting type generators which develop high kinetic energy or in cases where the device is being operated on rough, uneven terrain.
It is therefore a general object of the present invention to provide an acoustic pulse generator of the type described with improved means for mounting the generator on a transporting vehicle and for deploying the generator in a firing position.
It is a more particular object of the present invention to provide improved means for deploying a transportable acoustic generator of the type described wherein means are provided for minimizing lateral instability of the entire system.
With further reference to prior acoustic pulse generators of the type described, it has been found desirable to repeatably produce pulses of constant energy content. The energy developed depends upon the attained kinetic energy of the impacting mass or piston at the moment of contact with the target plate. If the driving gas pressure is held relatively constant, which is quite easily accomplished, this kinetic energy is a function of the distance that the impact piston travels. Thus it is important to insure that this distance does not vary from shot to shot. If the target plate rests on relatively soft ground, or tends to sink after several shots, this distance will tend to vary unless corrective measures are applied. More importantly, repeatable time delays from radio controlled trigger release to impact of the driven mass upon the target plate are required to simultaneously operate multiple sources or in a desired coded sequence. Constant energy content is also dependent upon maintenance of proper alignment between impact mass and target plate. If at any stage in the firing sequence this alignment is altered, the target plate may not receive a direct blow.
It is therefore a still further object of this invention to provide deployment means for a transportable acoustic pulse generator wherein impact mass travel distance remains constant from shot to shot, and proper mass to target alignment is maintained.
These and further objects and advantages of the present invention will become apparent from a consideration of the detailed description and drawings to follow.